double + cout

double a =  48.799999999999997;
cout << a;

double a =  48.799999999999997;
cout.precision(20);
cout << a;

#include <iostream>
#include <iomanip>
 
int main()
{
  std::cout.precision(5);
  std::cout << 5.123456789 << "\n";
  std::cout << std::setprecision(3) << 5.123456789 << "\n";
  std::cout << 5.123456789 << "\n";
}

#include <iostream>
#include <sstream>
using namespace std;
 
void Out(double out, int prec)
{
    ostringstream oss;
    oss.precision(20);
    oss << out;
    string out_s = oss.str(), out_o;
    for(unsigned int j = 0; j < out_s.length(); ++j)
    {
        out_o += out_s[j];
 
        if(out_s[j] == '.')
        {
            for(unsigned int i = j+1; i < j + prec + 1 && i < out_s.length(); ++i)
            {
                out_o += out_s[i];
            }
            
            goto qwe;
        }
    }
 
    qwe:;
    cout << out_o;
}
 
 
int main()
{
    Out(48.7999999999999, 5);
 
    cout << "\n\n";
    system("pause");
    return 0;
}